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   "source": [
    "# Copyright 2014 Brett Slatkin, Pearson Education Inc.\n",
    "#\n",
    "# Licensed under the Apache License, Version 2.0 (the \"License\");\n",
    "# you may not use this file except in compliance with the License.\n",
    "# You may obtain a copy of the License at\n",
    "#\n",
    "#     http://www.apache.org/licenses/LICENSE-2.0\n",
    "#\n",
    "# Unless required by applicable law or agreed to in writing, software\n",
    "# distributed under the License is distributed on an \"AS IS\" BASIS,\n",
    "# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n",
    "# See the License for the specific language governing permissions and\n",
    "# limitations under the License.\n",
    "\n",
    "# Preamble to mimick book environment\n",
    "import logging\n",
    "from pprint import pprint\n",
    "from sys import stdout as STDOUT"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### returning None is error prone!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Example 1\n",
    "def divide(a, b):\n",
    "    try:\n",
    "        return a / b\n",
    "    except ZeroDivisionError:\n",
    "        return None\n",
    "\n",
    "assert divide(4, 2) == 2\n",
    "assert divide(0, 1) == 0\n",
    "assert divide(3, 6) == 0.5\n",
    "assert divide(1, 0) == None"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Invalid inputs\n"
     ]
    }
   ],
   "source": [
    "# Example 2\n",
    "x, y = 1, 0\n",
    "result = divide(x, y)\n",
    "if result is None:\n",
    "    print('Invalid inputs')\n",
    "else:\n",
    "    print('Result is %.1f' % result)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### This is WRONG!!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Invalid inputs\n"
     ]
    }
   ],
   "source": [
    "# Example 3\n",
    "x, y = 0, 5\n",
    "result = divide(x, y)\n",
    "if not result:\n",
    "    print('Invalid inputs')  # This is wrong!\n",
    "else:\n",
    "    assert False"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "(True, 0.0)\n"
     ]
    }
   ],
   "source": [
    "# Example 4\n",
    "def divide(a, b):\n",
    "    try:\n",
    "        return True, a / b\n",
    "    except ZeroDivisionError:\n",
    "        return False, None\n",
    "print(divide(0, 5))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Invalid inputs\n"
     ]
    }
   ],
   "source": [
    "# Example 5\n",
    "x, y = 5, 0\n",
    "success, result = divide(x, y)\n",
    "if not success:\n",
    "    print('Invalid inputs')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Invalid inputs\n",
      "Invalid inputs\n"
     ]
    }
   ],
   "source": [
    "# Example 6\n",
    "x, y = 5, 0\n",
    "_, result = divide(x, y)\n",
    "if not result:\n",
    "    print('Invalid inputs')  # This is right\n",
    "\n",
    "x, y = 0, 5\n",
    "_, result = divide(x, y)\n",
    "if not result:\n",
    "    print('Invalid inputs')  # This is wrong"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Example 7\n",
    "def divide(a, b):\n",
    "    try:\n",
    "        return a / b\n",
    "    except ZeroDivisionError as e:\n",
    "        raise ValueError('Invalid inputs') from e"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {
    "collapsed": false
   },
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Result is 2.5\n"
     ]
    }
   ],
   "source": [
    "# Example 8\n",
    "x, y = 5, 2\n",
    "try:\n",
    "    result = divide(x, y)\n",
    "except ValueError:\n",
    "    print('Invalid inputs')\n",
    "else:\n",
    "    print('Result is %.1f' % result)"
   ]
  }
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